A prior art etching system is provided with an upper electrode and a susceptor serving as a lower electrode disposed opposite to each other in a processing chamber formed in an airtight processing vessel. When subjecting a workpiece to a predetermined etching process by this etching system, the workpiece is mounted on the susceptor, a predetermined process gas is supplied into the processing chamber and the workpiece is etched for the predetermined etching process by a plasma produced in the processing chamber by applying a predetermined radio frequency power across the upper electrode and the susceptor. The process gas is supplied through a gas supply pipe connected to gas sources, for example, into a space defined between the upper electrode and an upper electrode holding member holding the upper electrode, and then the process gas is discharged through a plurality of gas discharge holes formed in the upper electrode into the processing chamber.
Since a surface of the upper electrode facing the susceptor is exposed to the plasma, it is possible that an electric field is concentrated on the gas discharge holes, more specifically on the edges of the gas discharge holes on the side of the processing chamber, whereby the edges of the gas discharge holes are etched and particles are produced. If the particles adhere to the workpiece, the yield of the products of the etching system is reduced. A technique disclosed in, for example, JP-A No. 61-67922 inserts insulating members each provided with a through hole and formed of a ceramic material, such as alumina, or a fluorocarbon resin, such as Teflon in the gas discharge holes to prevent the concentration of an electric field on the gas discharge holes. The gas discharge holes are tapered toward the processing chamber, and the insulating members substantially tapered so as to conform with the tapered gas discharge holes are inserted downward from the upper end of the gas discharge holes in the gas discharge holes. The insulating members are fitted in the gas discharge holes so that the lower end surfaces thereof on the side of the processing chamber are flush with the surface of the upper electrode facing the susceptor. Thus, the insulating members are not caused to fall off the upper electrode toward the lower electrode by the pressure of the process gas, and prevent the concentration of an electric field on the gas discharge holes.
Since the insulating members are inserted in the gas discharge holes from the upper side of the upper electrode, the upper electrode needs to be removed from the processing vessel every time the insulating members are changed and hence the work for changing the insulating members takes much time, the operating time of the etching system is reduced accordingly, reducing the throughput of the etching system. Since the processing chamber is heated at a high temperature during the processing operation of the etching system, thermal stress is induced in the upper electrode. Consequently, the gas discharge holes and the insulating members are strained and, sometimes, the lower end surfaces of the insulating members on the side of the processing chamber are dislocated from a plane including the lower surface of the upper electrode facing the lower electrode.
Sometimes, the edges of the through holes of the insulating member on the side of the processing chamber are etched by the plasma produced in the processing chamber and particles are produced. Since the insulating members are made of alumina or a fluorocarbon resin, it is possible that particles of aluminum or the fluorocarbon resin are produced, and the particles adhere to the workpiece and exert adverse effects, such as the reduction of insulating strength, on the workpiece.
In a processing system provided with an upper electrode comprising an upper electrode member and a cooling plate placed on the upper electrode member, both the upper electrode member and the cooling plate are provided with a plurality of gas discharge holes. In this processing system, a plasma produced in a processing chamber flows through the gas discharge holes formed in the upper electrode member and the gas discharge holes of the cooling plate are damaged by the plasma.